Boko Haram leader Abubakar Shekau wants to be Africa's Osama Bin Laden, and has ratcheted up his anti-American rhetoric in an effort to spread his influence globally, according to a more-nuanced profile of him developed since he orchestrated the kidnapping of hundreds of Nigerian schoolgirls more than a month ago.

U.S. counterterrorism officials and terrorism experts say that Shekau, whose age is unknown and background mysterious, has developed a sophisticated media operation aimed at helping him achieve that goal. But they are divided on his ability to become an influential leader of militant Islam, with some calling him mentally unstable while others argue he is "crazy like a fox."

Shekau's best-known crime is the kidnapping of more than 300 Nigerian girls - 276 of whom remain missing -- from a government-run secondary school in Chibok on April 14. But under his command, Boko Haram has become the most violent terrorist group in the world, carrying out a laundry list of atrocities in northeastern Nigeria.

'A bin Laden wannabe'

But now, the man who is - at least for now -- perhaps the world's most sought after terrorist, is increasingly emulating Osama Bin Laden in an effort to increase his influence, the experts say.

"His entire on-stage persona is that of a bin Laden wannabe, from the weapon-wielding backdrops, the incessant video releases, etc.," said Emmanuel Ogebe, a Nigerian human rights lawyer who has long studied Boko Haram.

In recent video messages, Shekau has also become increasingly anti-American, specifically denouncing President Barack Obama in angry and dismissive terms and making aggressive statements " very much in the global jihadist vein, including threats against the U.S. from Shekau himself," said one U.S. counterterrorism official, speaking on condition of anonymity.

That leads one former U.S. ambassador to Nigeria believes an attack on U.S. interests in Nigeria is "inevitable."

Shekau is believed to be in his late 30s. Not only is his birthdate unknown, but there is doubt about where he was born. Most accounts have him being born in the nearby Republic of Niger, but Niger, which wants nothing to do with him, says he was born in Nigeria's Yobe State. His mother has long lived in the Nigerian city of Maiduguri, not far from where the girls were grabbed.

His early years also are wrapped in mystery. He received little formal education, but because of a photographic memory, learned to speak multiple languages -- Hausa, the main language of north Nigeria, a little English, "very good Arabic," as well as his native Kuneri, said one U.S. official.

In the latter half of the last decade, he gave fiery sermons in the main mosque in Maiduguri, which were taped and widely distributed. In them, he railed against Western education, music, and called for the imposition of sharia law, all now the tenets of Boko Haram.

Most violent terror group

He rose to prominence in 2009, when his mentor, Mohammad Yusuf, was killed by Nigerian police. At that time, Boko Haram leaders were involved "in a leadership tussle for who could be the most violent," says Ogebe. Shekau won.

Once in charge, Shekau became far more radical than Yusuf and bolstered the group's operational capability, revitalizing it, according to a U.S. intelligence official, who spoke with NBC News on condition of anonymity.

Since his ascent to power, Boko Haram has become the most violent terrorist group in the world, according to the Council on Foreign Relations, killing more than 7,000 people. That bloody toll has prompted the U.S. to place a $7 million bounty on Shekau under the Rewards for Justice program.

A boy walks past burnt shops at Ngumborum central Market in the northeastern Nigerian city of Ngala on May 11, six days after they were attacked by suspected Boko Haram insurgents.AFP - Getty Images

At the same time, say U.S. officials, he has attempted to shape the group in the mold of al Qaeda and its affiliates. In August 2011, for example, Gen. Carter Ham, then head of the U.S. Africa Command, stated that Shekau had forged increasing ties with the Mali-based Al Qaeda in the Islamic Magreb (AQIM) terror group.

"He has definitely been key not just to an ideological alignment with al Qaeda but also in adopting al Qaeda-like tactics," says Michael Leiter, former director of the National Center for Counter Terrorism and now an NBC analyst, referring to his use of spectacular attacks. However, even al Qaeda has criticized some of those attacks for their brutality, particularly the burning of an elementary school filled with young boys.

One area where he does not emulate al Qaeda is his leadership style. Whereas Bin Laden would often consult a small circle of advisers, Shekau is autocratic.

"Shekau's leadership style is as rigid as his ideology," said the counterterrorism official. "He surrounds himself with yes-men and rejects as apostates anyone who would question his authority. Shekau's bloodthirsty and unflinching campaign against largely civilian targets — including elementary school s—in part led to the emergence in 2012 of a splinter faction (of Boko Haram)."

Added Ogebe,"Shekau has leap-frogged the organization from a rag-tag matchete-wielding, small-arms shooting, and petrol-bombing (group) to an RPG-firing, (car bombing) and IED-deploying fighting force."

Mad or 'crazy like a fox'?

Shekau's stability is one point of disagreement among the experts.

"Any impartial observer — especially those who have watched his public statements over the years— would be left wondering about Shekau's mental state, especially after his most recent video appearance," said a senior U.S, counter terrorism official, referring to a tape in which a rambling, wild-eyed and gesticulating Shekau demandied the release of Boko prisoners before returning the girls.

But those who dismiss Shekau as deranged miss how resonant his overall message of greater commitment to Islam is to his target audience, the Muslims of northern Nigeria, says John Campbell, U.S. ambassador to Nigeria between 2004 and 2007. He calls Shekau "crazy like a fox. Look at his media skills."

Campbell says Shekau is focusing the widespread anger in northern Nigeria, which is overwhelmingly Muslim -- and poor. "The outrageous rhetoric that others dismiss is extremely attractive to illiterate people who've been ground down and are angry ... and he is fully enjoying it."

Campbell adds that mirroring Osama bin Laden's style in the region is a positive for Shekau. "Bin Laden is widely admired in northern Nigeria," he said. "You see pictures of OBL all over the place."

Campbell also points to the sophistication of the group's "elaborate media operation." It releases videos very quickly after attacks on Nigerian government facilities and Shekau's appearance "demonstrates a fair amount of presence, with some composition to the video." Unlike al Qaeda leader like Bin Laden or Ayman al-Zawahiri, Shekau's face will often fill the screen, he notes. He gestures frequently, his voice rising and sometimes switching languages.

His threats aimed at the U.S. have also been accompanied by actions, though limited to Boko Haram's current theater of operations.

Ogebe points to one example, from August 2011, when Boko Haram killed 23 people in a bombing of a United Nations building in the Nigerian capital of Abuja, an attack in which two Americans inside escaped harm. "They specifically addressed their message to President Obama. They have called him to convert to Islam," he said.

He also said the group also has carried out attacks near the U.S. Embassy in Abuja and has attempted to kidnap American aid workers in northern Nigeria in recent years.

Campbell says the recent "open and public condemnations by the United States, the United Kingdom, France and Israel is likely to push or strengthen international links. I would anticipate anti-American rhetoric to increase and that an attack on some kind of U.S. interest in northern Nigeria is inevitable," he said.